1. Field of the Invention
The present invention relates to an acoustic wave device, and more specifically to an acoustic wave device including a cavity provided between a support substrate and a piezoelectric substrate, and to a manufacturing method for the acoustic wave device.
2. Description of the Related Art
International Publication No. WO2010/082571 discloses an acoustic wave device utilizing a plate wave. In manufacturing this acoustic wave device, a multilayer body is prepared in which a sacrificial layer is formed in a recess in an upper surface of a support substrate and a piezoelectric single-crystal substrate is laminated in a state covering the sacrificial layer. In the multilayer body, an interdigital transducer (IDT) electrode is previously formed on a surface of the piezoelectric substrate, the surface facing the sacrificial layer. At least one through-hole is formed in the piezoelectric substrate to be communicated with the sacrificial layer. The sacrificial layer is removed by etching via the through-hole. As a result, a space occupied so far by the sacrificial layer is formed as a cavity. The IDT electrode provided on the piezoelectric substrate is positioned facing the cavity.
In the acoustic wave device disclosed in International Publication No. WO2010/082571, the through-hole is formed in order to remove the sacrificial layer. Therefore, the IDT electrode is apt to contact with open air via the through-hole. This causes a problem that weather resistance of the IDT electrode reduces, namely that deformation, color change, degradation, and so on of the IDT electrode occur.